Epidermal squamous cell carcinoma (SCC) is among the most frequent of cancers. It is treated by surgical excision, but the recurrence and metastatic rates approach 10%. Our scientific premise is that human epidermal cancer stem (ECS) cells are formed early in skin cancer and these cells are important cancer prevention targets. An important goal in this context is identifying and inhibiting activity of key proteins that are elevated and essential for ECS cell survival. Of particular interest, we show that tissue transglutaminase (TG2), an emerging cancer stem cell survival regulator, is highly elevated in ECS cells as compared to non- stem cancer cells. Of further importance, TG2 knockdown or treatment with sulforaphane (SFN), a promising diet-derived cancer prevention agent, reduces TG2 activity which is associated with reduced ECS cell survival and additional new studies indicate that TG2-knockout markedly reduces ECS cell tumor formation. We also provide new data suggesting that SFN covalently modifies TG2 to shifts its structure to an open inactivate conformation. These novel findings suggest that SFN treatment converts TG2 from a closed (GTP binding, signaling) pro-ECS cell survival form to an open inactive conformation. Our goal is to characterize this unique regulation to provide new understanding of how SFN influences this important target. We will test the idea that SFN treatment may regulate TG2 structure via mechanisms that involve direct covalent modification, and study the role of TG2 as a mediator of SFN action and a SFN treatment target in cultured ECS cells and tumors.